Switched capacitor amplifier circuit, voltage amplification method, and infrared sensor device

A switched capacitor amplifier circuit configured to perform a first operation and a second operation, the first operation being configured to retain an electric charge corresponding to an input voltage upon reception of said input voltage from a signal source, the second operation being configured to amplify said input voltage and to output the amplified input voltage as an output voltage, the switched capacitor amplifier circuit comprising:

• an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, the operational amplifier being configured to output said output voltage from said output terminal;
• a first capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a second capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a first switching circuit configured to connect the second end of said first capacitor to a fixed potential during said first operation, and to connect the second end of said first capacitor and said signal source during said second operation;
• a second switching circuit configured to connect the second end of said second capacitor to said fixed potential while short-circuiting said output terminal and said negative input terminal of said operational amplifier during said first operation, and to connect the second end of said second capacitor and said output terminal of said operational amplifier so as to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor during said second operation;
• and
• an impedance converter circuit configured to convert an output impedance of said signal source into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor.

A switched capacitor amplifier circuit configured to perform a first operation and a second operation, the first operation being configured to retain an electric charge corresponding to an input voltage upon reception of said input voltage from a signal source, the second operation being configured to amplify said input voltage and to output the amplified input voltage as an output voltage, the switched capacitor amplifier circuit comprising:

• an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, the operational amplifier being configured to output said output voltage from said output terminal;
• a first capacitor having a first end and a second end, the first end being connected to said positive input terminal of said operational amplifier;
• a second capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a third capacitor having a first end connected to said negative input terminal of said operational amplifier and a second end connected to a fixed potential;
• a first switching circuit configured to connect the second end of said first capacitor and said signal source during said first operation, and to connect the second end of said first capacitor to said fixed potential during said second operation;
• a second switching circuit configured to connect the second end of said second capacitor to said fixed potential while short-circuiting said output terminal and said negative input terminal of said operational amplifier during said first operation, and to connect the second end of said second capacitor and said output terminal of said operational amplifier so as to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor during said second operation;
• and
• an impedance converter circuit configured to convert an output impedance of said signal source into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor.

A switched capacitor amplifier circuit configured to perform a first operation and a second operation, the first operation being configured to retain an electric charge corresponding to an input voltage upon reception of said input voltage from a signal source, the second operation being configured to amplify said input voltage and to output the amplified input voltage as an output voltage, the switched capacitor amplifier circuit comprising:

• an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, the operational amplifier being configured to output said output voltage from said output terminal;
• a first capacitor having a first end and a second end, the first end being connected to said positive input terminal of said operational amplifier;
• a second capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a third capacitor having a first end connected to said negative input terminal of said operational amplifier and a second end connected to a fixed potential;
• a first switching circuit configured to connect the second end of said first capacitor to said fixed potential during said first operation, and to connect the second end of said first capacitor and said signal source during said second operation;
• a second switching circuit configured to connect the second end of said second capacitor to said fixed potential while short-circuiting said output terminal and said negative input terminal of said operational amplifier during said first operation, and to connect the second end of said second capacitor and said output terminal of said operational amplifier so as to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor during said second operation;
• and
• an impedance converter circuit configured to convert an output impedance of said signal source into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor.

A switched capacitor amplifier circuit configured to perform a first operation and a second operation, the first operation being configured to retain an electric charge corresponding to a first input voltage upon reception of the first input voltage from a first signal source and to retain an electric charge corresponding to a second input voltage upon reception of the second input voltage from a second signal source, the second operation being configured to amplify a difference between said first input voltage and said second input voltage and to output the amplified difference as an output voltage, the switched capacitor amplifier circuit comprising:

• an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, the operational amplifier being configured to output said output voltage from said output terminal;
• a first capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a second capacitor having a first end connected to said negative input terminal of said operational amplifier;
• a third capacitor having a first end and a second end, the first end being connected to said positive input terminal of said operational amplifier;
• a first switching circuit configured to connect the second end of said first capacitor and said first signal source during said first operation, and to connect the second end of said first capacitor to a fixed potential during said second operation;
• a second switching circuit configured to connect the second end of said second capacitor to said fixed potential while short-circuiting said output terminal and said negative input terminal of said operational amplifier during said first operation, and to connect the second end of said second capacitor and said output terminal of said operational amplifier so as to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor during said second operation;
• and
• a third switching circuit configured to connect a second end of said third capacitor to said second signal source during said first operation, and to connect the second end of said third capacitor to said fixed potential during said second operation;
• and
• an impedance converter circuit configured to convert an output impedance of said first signal source and said second signal source into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor and between said third switching circuit and the second end of said third capacitor.

A voltage amplification method in a switched capacitor amplifier circuit, the switched capacitor amplifier circuit including an operational amplifier configured to output an output voltage, a first capacitor having a first end connected to a negative input terminal of said operational amplifier, a second capacitor having a first end connected to the negative input terminal of said operational amplifier, a first switching circuit configured to switch a connection destination of a second end of said first capacitor to a signal source or a fixed potential, a second switching circuit configured to switch a connection destination of a second end of said second capacitor to said fixed potential or an output terminal of said operational amplifier while short-circuiting between said output terminal and said negative input terminal of said operational amplifier, or to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor, an impedance converter circuit configured to convert an output impedance of said signal source into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor, the voltage amplification method comprising the steps of:

• connecting said signal source and an input terminal of said impedance converter circuit, short-circuiting said output terminal and said negative input terminal of said operational amplifier, and connecting the second end of said second capacitor to said fixed potential;
• and
• connecting said input terminal of said impedance converter circuit to said fixed potential, and connecting said negative input terminal and said output terminal of said operational amplifier through said second capacitor.

An infrared sensor device configured to detect a surface temperature of a measurement target on a basis of an infrared ray radiated from said measurement target, the infrared sensor device comprising:

• a thermopile configured to generate a measurement voltage indicative of said surface temperature;
• an amplifier circuit configured to amplify said measurement voltage to generate an output voltage, wherein
• the amplifier circuit is a switched capacitor amplifier circuit configured to perform a first operation and a second operation, the first operation being configured to retain an electric charge corresponding to said measurement voltage upon reception of said measurement voltage from said thermopile, the second operation being configured to output said output voltage,
• the switched capacitor amplifier circuit includes:
• an operational amplifier having a positive input terminal, a negative input terminal, and an output terminal, the operational amplifier being configured to output said voltage terminal from the output terminal;
• a first capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a second capacitor having a first end and a second end, the first end being connected to said negative input terminal of said operational amplifier;
• a first switching circuit configured to connect the second end of said first capacitor and said thermopile during said first operation, and to connect the second end of said first capacitor to a fixed potential during said second operation;
• a second switching circuit configured to connect the second end of said second capacitor to said fixed potential while short-circuiting said output terminal and said negative input terminal of said operational amplifier during said first operation, and to connect the second end of said second capacitor and said output terminal of said operational amplifier so as to connect said output terminal and said negative input terminal of said operational amplifier through said second capacitor during said second operation;
• and
• an impedance converter circuit configured to convert an output impedance of said thermopile into a specified impedance, the impedance converter circuit being connected between said first switching circuit and the second end of said first capacitor.